1. Field of the Invention
The present invention relates to an improved sulfur solvent system for use in high temperature, high pressure wells. More specifically, it is concerned with a fatty amine activated dialkyl disulfide oil capable of sustaining a liquid sulfur dissolving phase at high temperature, high pressure bottomhole conditions.
2. Description of the Prior Art
The problems associated with sulfur depositing and accumulating in sour gas distillate wells which result in plugging the formation, tubing string, and surface equipment and reducing the desired flow of fluids therefrom, are well known. Whenever a natural formation contains high concentrations of hydrogen sulfide and elemental sulfur, safeguards to inhibit the precipitation of elemental sulfur and methods to remove sulfur blockage during production are employed. The prior art proposes various methods for using various types of sulfur solvents, for example, aromatic hydrocarbons such as benzene, toluene, xylene, and naptha, and the classical sulfur solvent carbon disulfide. Thus, U.S. Pat. No. 3,744,565 teaches the use of a saturated and unsaturated cyclohydrocarbon while U.S. Pat. No. 3,393,733 exemplifies the use of carbon disulfide.
During the past decade, various methods based on the ability of elemental sulfur to form polysulfides and thus be removed in the polysulfide form have been suggested and have experienced limited commercial success. In U.S. Pat. No. 3,331,657 an aqueous alkali metal or ammonium hydroxide caustic solution is employed to react, in situ, with hydrogen sulfide forming the corresponding alkali sulfide which then prevents or removes elemental sulfur by forming the polysulfide. U.S. Pat. No. 3,909,422 suggests a further improvement in the inorganic caustic reaction by employing a wetting agent in combination with the alkali hydroxide. Similarly, U.S. Pat. No. 3,545,916 proposes the use of a basic aqueous solution containing high concentrations of either an alkyl amine (e.g., ethyl amine, etc.) or aromatic nitrogen containing heteronuclear cyclic compound (e.g., pyridine, etc.) to prevent the precipitation of sulfur by virtue of the formation of polysulfides. In U.S. Pat. No. 3,913,678, the polysulfide forming property of ethyl amine is again employed in combination with a complexing agent such as EDTA to inhibit scale formation and sulfur deposits during sour gas well production. While in U.S. Pat. No. 3,531,160, elemental sulfur deposits in sour gas-sulfur wells is removed by circulating a liquid alkyl sulfide, alkyl disulfide, or alkyl polysulfide in the well.
U.S. Pat. No. 3,846,311, which involves a common coinventor relative to the present invention, is of particular interest to the present invention in that it represents the starting point from which the present invention developed. In this commonly assigned patent, a method for increasing the amount of sulfur which a given quantity of dialkyl disulfide solvent will dissolve is disclosed. The method requires that the dialkyl disulfide be catalyzed by the addition of a small amount of a lower aliphatic amine followed by an aging process. Such a solvent, produced in accordance with this reference, will exhibit an outstanding ability to dissolve sulfur with ultimate sulfur solubilities of as high as five times as much sulfur being dissolved on a weight basis as there was weight of original dialkyl disulfide. Such compositions have now been employed commercially to replace the more dangerous carbon disulfide sulfur solvents. However, the commercial success has been somewhat limited in that certain high temperature, high pressure ultra deep sour gas wells have been encountered wherein the amine activated dialkyl disulfide solvents have been ineffective, thus necessitating a resumption of the use of carbon disulfide solvent. It is presently felt that the failure of the amine activated dialkyl disulfide solvents in the high temperature, high pressure wells can be directly attributed to the fact that these previous sulfur solvents do not create sufficient liquid phase at bottomhole conditions to be effective in removing the sulfur deposits.
With ever increasing world energy demands and the advent of international fuel shortages, the oil and gas industry has been forced to drill deeper and deeper into more hostile environments in search of critically needed fuel. As a result, high temperature, high pressure deep horizon sour gas fields, potentially involving gas wells of interest in the present invention, have been discovered throughout the world. For example, high pressure deep sour gas wells have been encountered in Canada, France, West Germany, and Austria, as well as in Mississippi, Texas, and Oklahoma. As a general rule of thumb, at bottomhole temperatures in excess of 250.degree. F. and bottomhole pressures of the order of 4000 psi, one can anticipate sulfur deposit removal problems during production. Such conditions are now being frequently exceeded, particularly when the depth of the well approaches 20,000 ft.